NCEES Construction PM Problem #532

[Kicho]

Need your help on NCEES Construction PM problem #532. I have no clue how to use the given talbe to solve this problem. Thank you in advance.

#532

A multistory concrete building is being constructed using two level of shores and forms and two levels of reshores. Construction has been completed through Level 8 as shown in the figure. An analysis has been made to the step shown using the assumption that the shores and reshores are infinitely stiff, the slabs and forces are expressed as a multiple of the typical floor dead load, D. The forms and shores combined weight 0,10D at each level installed, and the reshores weigh 0.05D at each level installed. At the end of the previous oeration shown, there is no worker live load. In the next operation, the forms and shores between Levels 6 and 7 are stripped, lown upward, and stored on top of Level 8 for re-erection. The load of workers imposed on Levels 6 and 8 during this next operation is 0.40D on each. The reshores will be moved from between Levels 4 and 5 tp betweem 6 and 7 in a future operation.

As the operation to move the forms and shores from between Levels 6 and 7 to Level8 is ending, but while the workers are still on the floor at Level 8, the load carried by the floor at Level 7 is most nearly:

a. 1.40D

b. 1.45D

c. 1.65D

d. 1.70D

Shore

Loads

Before

step Loads Carrid by Floor in Multiples of D Shore

Loads

After

Step Before

Step Change During Step After Step 0.0D 1.10D 0.70D 1.50D 1.90D 0.65D 1.25D 0.45D 1.45D

 

[Kicho]

sorry the excel table didn't work on this format...

is there any ways to attach the excel sheet?

 

[Construction PE]

Hi Kicho. Here are the basics on how to use the given table:

The second column from left to right "Loads carried... before step" refer to each of the slabs.

So the top number 0.0D means slab 8 carries 0 load.

The number below that "0.70D" means slab 7 carries .7D

Slab 6 carries 1.90D and so on.

The first column "Shore loads before step" is similar only it refer to the loads in between the slabs (carried by shoring or reshoring).

So the first number listed "1.10D" is the load carried by the shores in between slabs 7 & 8.

1.50D is the load carried by the shores in between slabs 6 & 7 etc.

So how to solve this particular problem...

The table gives you all of the loads as the figure is currently drawn... before anything is shifted around. Well the problem tells you you will remove the forms and shores from between Levels 6 & 7 and move them and ultimately you want to determine the load on Level 7 after all is said and done.

Step 1. Remove shores from between 6 & 7. You end up with no support there so slab 7 deflects a little bit under it's weight and the weight of everything that is above it. So the load that was originally carried by the 6-7 shores (which was 1.5D given by the table) is now carried partly by slab 7 & partly by slab 8 (minus the self-weight of the shores which are currently removed from the building). Essentially 1.5D load previously carried by shores - 0.1D self weight of the shores = 1.4D divided by 2 slabs= 0.70D of that load is carried by slab 7.

Step 2. Fly the 6-7 shores up to the top of the structure and store them for use on top of slab 8. So the weight of the shores is now distributed and carried by slabs 7 & 8. So the weight of the shores 0.10D divided by 2= 0.05D is now also carried by slab 7.

Step 3. Now you get construction workers on top of slab 8. This load is 0.40D as stated in the problem... also carried by slabs 7 & 8. So 0.40D divided by 2= 0.20D carried by slab 7.

So the total:

Slab 7 = 0.70D carried by this slab before anything changed (from the table)+ 0.70D added by removing the 6-7 shores (Step 1 above) + 0.05D added by stacking the shores on slab 8 (Step 2 above) + 0.20D added by the construction workers (step 3 above) = 1.65D (answer)

Basically, all you need the chart for is to tell you how much load is on your slab at this point (before anything changes) and how much load is on the shoring or restoring (that will need to be distributed once they are removed).

If you have the ACI SP-4 code listed in the NCEES construction references, I would recommend reading through Tables 5-2, 5-2A, 5-3, and 5-3A and the paragraphs before each of these tables. This explains how the charts work and how each removal or addition of shoring, restoring, manpower etc affects the loads on the structure.

Hope this helps!

 

[Kicho]

Thanks Field Tech!!!

 

[Kicho]

oops, Frustrated Studying was the handle name...

thank you for your help